1. Field of Invention
The invention relates to a bottle top dispenser for handling liquids. In these appliances, it is important to have an exact metering and conveyance of liquids out of a storage bottle or another storage container. Exact metering taking place when a volume of liquid is taken up from the supply bottle or the like into the appliance and/or when a volume of liquid is dispensed from the appliance outward into a container.
2. Description of Related Art
Bottle top dispensors of the type in question are used comprehensively in chemistry, biology and pharmacy in the laboratory and in production.
The term “liquid” designates, in the present context, liquids, such as are used comprehensively in chemistry, biology, pharmacy, etc., in the laboratory and in production, in particular, liquids with a relative viscosity of up to about 300 (viscosity in relation to the viscosity of water under normal conditions). Therefore, the liquids range from very thin flowing liquids to slightly thick-flowing ones.
A manually operable burette serves, during titration, for determining the unknown quantity of a dissolved substance from the consumption of a reagent liquid of known concentration. In order to ensure expedient and efficient analysis work, a burette must satisfy the requirements of a rapid and accurate dispensing and indication of the specific liquid quantity. In this case, high demands are made as to the precision of the dispensing of liquid and as to operator safety (General Catalogue 600 “Laborgeräte von Brand” [“Brand Laboratory Appliances”] of BRAND GMBH+CO KG 09/01, No. 9963 00, “Burette Digital III”, pages 27 to 34).
Comparable demands are also found in bottle top dispenser dispensers, particularly in those with a digital indication of the desired metering volume (DE-A-35 16 596; General Catalogue 600 “Laborgeräte von Brand” [“Brand Laboratory Appliances”] of BRAND GMBH+CO KG 09/01, No. 9963 00, “Dispensette”, pages 9 to 18).
Hereafter, the bottle top dispenser is described in its operating position, that is to say in its position fastened on a storage bottle and oriented essentially vertically.
The valve block usually has located in it a suction intake valve which makes it possible to suck in liquid from the storage bottle by means of a suction intake pipe. A discharge line with a discharge valve located in it extends approximately horizontally from the valve block. Since the discharge line projects approximately horizontally from the valve block and often also carries an additional changeover valve, this is the side from which an operator works with the bottle top dispenser. This side is therefore designated hereafter as the “front side” or as the “front.” The opposite side is the “back side” or “rear.” In a bottle top dispenser, an indicator with corresponding operating elements is usually located in front.
The known bottle top dispenser for handling liquids, from which the invention proceeds (see the General Catalogue 600 “Burette Digital III”, as given above), is distinguished in that the cylinder/piston arrangement is overmounted from above by an outer housing closed on top. This outer housing moves upward, with respect to the cylinder, together with the piston rod. In order to implement this, the cylinder has located on it a vertically running rack, with which meshes a pinion on a driveshaft which is mounted in the outer housing. The piston drive of this bottle top dispenser is designed for manual actuation, and therefore the driveshaft carries a manual actuation knob there at each of the two ends outside the outer housing.
The precise advantage of this bottle top dispenser is that the outer housing is closed around the cylinder/piston arrangement. However, this, is at the expense of the movement of the overall outer housing, together with all the subassemblies arranged in it. Particularly in the position in which the outer housing is moved fully upward, such an arrangement of the bottle top dispenser and storage bottle has a considerable tendency to tilt.
A similar design with a corresponding tendency to tilt is also found in other bottle top dispensers (German Patent Applications DE-A-35 16 596 and DE-A-35 34 550).
Another solution is found in a bottle top dispenser in the form of a piston burette with digital indication, in which a housing receiving the piston drive, the indicator, a sensor arrangement and control electronics is in a fixed invariable relative position with respect to the valve block (German Patent DE-C-35 01 909). Here, however, the outer housing is not closed, but, instead, the piston rod passes through the housing upward from below, even when the piston is in the lowest position in the cylinder. When the piston is moved up, the piston rod emerges from the housing on top. In this case, by means of an upwardly connected concertina, the ingress of dirt and dust via the passage orifice for the piston rod into the housing is prevented.
In the bottle top dispenser explained above, admittedly, the tendency to tilt is somewhat lower than in the bottle top dispenser from which the invention proceeds, because the outer housing is not displaced overall with respect to the valve block. However, this entails the structural disadvantage of the outer housing being open on top.
In all bottle top dispensers of the type in question, actuating buttons are located on the front side of the outer housing. An actuation of the actuating buttons in this case makes it necessary to prop up the outer housing, in any event if a tilting of the arrangement of the bottle top dispenser and storage bottle is to be reliably prevented. This is important particularly in the case of storage bottles of small volume.
Many influences in terms of design and of handling are important for the accuracy of a bottle top dispenser of the type in question. What is important, inter alia, is the stick/slip effect, that is to say the overcoming of the static friction of the piston in the cylinder at the transition to sliding friction during displacement. Many structural factors of the bottle top dispenser are involved here. Operator friendliness and operator safety are in this case essential boundary conditions.
The above-explained structural features of the known bottle top dispensers are relevant for operator friendliness and operator safety.
Furthermore, for accuracy and operator safety, the boundary conditions, under which bottle top dispensers of the type in question are often used, have to be taken into account.
As has already been referred to, it is advantageous to design the bottle top dispenser so as to be largely chemical-resistant. However, this does not only involve the surfaces coming into contact with the liquid. In fact, caustic or otherwise harmful liquids, of course, also generate corresponding vapors which may present problems in the inner space of the outer housing of the bottle top dispenser according to the invention.
In the abovementioned bottle top dispenser with a concertina, there is the particular problem that the vapors emanating from the wetting of the inner wall of the cylinder cannot escape. The space surrounding the piston rod is displaced by the piston during the suction intake operation. This atmosphere, in this case, escapes past the sensor system and coats it. The permanent action of these vapors on components of this type in a closed and non-actuated housing quickly leads to considerable operating faults.
The teaching of the present invention, then, is based on the problem of specifying a bottle top dispenser for handling liquids which achieves particularly high operator friendliness and operator safety.